Pretty sure you will have to have the BCM modified to allow the heated seats to work. I think they are connected to that somehow. This can be done with a Tech II scanner or at a GM dealer.
Um What?
No.
Heated seats have nothing to do with the BCM.
Wires go from fuse box to switch to seat heater. Easiest would be to grab the switch and the wiring going to the seat from the pick n pull.